This invention relates to a method of making an industrial mineral filler and a pozzolan product from fly ash, and more particularly, to a method in which raw fly ash is dry processed into fine and coarse fractions which can be utilized as mineral filler and pozzolan products.
Fly ash is a by-product derived from the combustion of coal and comprises finely divided inorganic products. Enormous amounts of fly ash are produced annually nationwide, primarily from burning coal in electric power plants. Disposal of fly ash has posed an increasingly difficult problem because the volume, the particulate nature, and the varied chemical composition of fly ash limit the number of acceptable disposal sites.
Accordingly, efforts have been made to find alternative, economic uses for fly ash. For example, fly ash has been used as a pozzolan material in concrete applications. However, the direct use of fly ash as a pozzolan product has been limited as the high carbon content in the fly ash prevents entrainment of the concrete, causing non-uniform hardening. In order for larger amounts of fly ash to be suitable for use as a pozzolan product, the fly ash should have a low carbon content.
Another potential use for fly ash is as an industrial mineral filler. Mineral fillers are widely used in plastic products to improve performance and reduce costs. Mineral fillers commonly used for applications such as plastics, compounding, injection molding, paper products and the like include calcium carbonate, kaolin, aluminum hydrate, mica, talc and ground silica. The chemistry and characteristics of fly ash are close to those of such commercial fillers and would be a desirable substitute. However, the particle size of fly ash is much larger than that of typical commercial fillers. Wet processing such as wet milling, froth flotation, attrition grinding, and wet magnetic iron removal have been used in the past to reduce and control the particle size of fly ash. However, such methods are complicated, expensive, and require a multi-step process as the wet fly ash must be oven dried. In addition, methods such as froth flotation utilize reagents such as turpentine which must be safely disposed of.
Accordingly, there is still a need in the art for a method for producing useful products from fly ash such as mineral filler and pozzolan which method is economical and easy to implement.